Eukaryotes early lineages

III. Domains Originating Early in Eukaryotic Lineage A. Horizontal Gene Transfer... 

Table I shows that many domain families are widespread among fungi, plants, and metazoa and yet are absent from prokaryotes. It is assumed that these domains arose in early eukaryotes before the emergence of these three major eukaryotic lineages. Consideration of the known functions of these domains, and the proteins in which they occur, strongly suggests that emergence of several cellular functions that are unique to eukaryotes occurred in early eukaryotic history. These functions are likely to have coevolved with the abilities of the protoeukaryotic cell to reproduce sexually and to partake in cell—cell communication. Here we review several eukaryotic-specific domain families as illustrations of the coevolution of domain families with cellular functions.

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